PS/CTAB/silica composites from room temperature polymerization of high internal phase emulsion gels

Synthesis of Polymers with Narrow Molecular Mass Distribution through Interface-Initiated Room-Temperature Polymerization in Emulsion Gels

Homopolymers of n-butyl acrylate, methyl methacrylate, styrene, and their random copolymers were prepared via interface-initiated polymerization of emulsion gels at 20 °C. The polymerization was conducted in a free radical polymerization manner without inert gas protection. Compared with the polymers synthesized at 60 °C, the polymerization of emulsion gels at 20 °C produced homo- and copolymers with a higher molecular mass and a narrower molecular mass distribution. The polydispersity indices for the polymers synthesized at 20 °C were found to be between 1.12 and 1.37. The glass transition temperatures for the as-synthesized butyl acrylate copolymers agree well with the prediction from the Gordon-Taylor equation. Interface-initiated room-temperature polymerization is a robust, energy-saving polymerization technique for synthesizing polymers with a narrow molecular mass distribution.

Low Temperature, In Situ Polymerization of Vinyl Acetate in Silica Containing Emulsion Gels

Vinyl acetate (VAc) was polymerized to about 90% conversion in 9 h at 40°C from the colloidal microstructure of the VAc/fumed silica/cetyltrimethylammonium bromide (CTAB) system. The glass transition ( $T_g$ ) of poly(vinyl acetate) (PVAc) polymerized in these emulsion gels with silica was higher ( $T_g={41}^{°}\text{C}$ ) than those of PVAc made from bulk polymerization at 60°C ( $T_g={31}^{°}\text{C}$ ) and the weight average molar mass ( $M_w$ ) was also larger ( $M_w$ about 300 kg/mol) than those from bulk polymerization ( $M_w=125\text{kg}/\text{mol}$ ). Increased $M_w$ , $T_g$ , and lowered processing temperature for these composites could facilitate new applications for PVAc.

Cationic surfactant blocks radical-inhibiting sites on silica

Surfactant-catalyzed room-temperature radical polymerization of methyl methacrylate (MMA) was conducted in the presence of fumed silica nanoparticles and water. Three types of surfactants, cationic (CTAB), nonionic (Triton X-100) or anionic (SDS), were used to catalyze the decomposition of the initiator, 2,2'-azobisisobutyronitrile (AIBN). The surfactant-catalyzed decomposition rate constant for AIBN at room temperature was found to be independent of the surfactant type. However, the rates of polymerization of the MMA emulsion gels at room temperature were found to depend on the types of surfactant with: cationic>nonionic>anionic. An inhibition period was observed for the polymerizations with nonionic and anionic surfactants. The radical-inhibition was likely due to the reactions between the radicals and the silanol groups on fumed silica. This inhibition can be reduced by using cationic surfactants to block these surface silanols.

Low-temperature polymerization of methyl methacrylate emulsion gels through surfactant catalysis

Poly(methyl methacrylate) (PMMA)/silica/cetyltrimethylammonium bromide (CTAB) composites were prepared through surfactant catalyzed free radical polymerizations at 40 °C. Fumed silica particles controlled the morphology of the polymeric composites producing porous structures. The internal structures of the porous composite were determined using temperature-modulated differential scanning calorimetry (TMDSC). The fumed silica particles were encapsulated by an incompletely covered CTAB monolayer, with a crystallization temperature, T(C,CTAB)=76 °C, and a mixed PMMA/CTAB shell, with T(C,CTAB)=63 °C. The fumed silica surfaces acted as inhibitors for PMMA free radical polymerizations. Much of the PMMA formed in the composites was adsorbed on the silica, as evidenced by its elevated glass transition temperature compared to bulk. The enhanced decomposition of the initiator was catalyzed by CTAB and resulted in free radical polymerization of PMMA at 40 °C, which is considerably lower than the temperatures normally used for PMMA synthesis by free radical means with thermal initiation. These lowered polymerization temperatures allow energy efficient production of composites, which can incorporate temperature sensitive materials.